A 98-year-old Hungarian who topped the list of the world’s most wanted Nazi war crimes suspects has died of pneumonia just weeks before he was due to stand trial accused of sending more than 15,000 Jews to the gas chambers of Auschwitz.

Laszlo Csatary, who had been suffering from a series of medical problems, died from pneumonia in hospital in Budapest on Saturday, his lawyer, Gabor Horvath, said. He had denied the allegations against him.

Csatary was named by the Simon Wiesenthal Centre, which is based in the US and hunts Nazis, as its most-wanted suspect in 2012. Efraim Zuroff, its director said that he was “deeply disappointed” at the news of Csatary’s death. “Csatary was a totally unrepentant Holocaust perpetrator who ultimately eluded justice and punishment at the very last minute,” he said. Prosecutors said that Csatary was a Hungarian police officer who was chief of an internment camp for Jews in Kosice, which was then part of Hungary but is now in Slovakia. He was accused of beating and torturing prisoners in the camp, which was the first to be established after the Germans occupied Hungary.

He was sentenced to death in absentia by a Czechoslovak court in 1948, after he had fled to Canada. He worked as an art dealer in Montreal and Toronto until he was unmasked by war crimes investigators in 1995. He fled to Hungary in 1997 after he was accused of lying about his Nazi past to obtain Canadian residency.

In 2012, the Simon Wiesenthal Centre discovered that he was living in Budapest. He was arrested in July 2012 and Hungarian prosecutors charged him with war crimes in June.

He faced charges of aiding and abetting the execution and torture of 15,700 Jews deported to Auschwitz and accusations of extreme brutality towards individual prisoners, including beating them with his fists and a dog whip.